Elucidation of the pathogenesis mechanism of viroids

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Elucidation of the pathogenesis mechanism of viroids ******Viroids infect higher plants and cause diseases that result in significant damages in agriculture, accounting for the loss of several billion dollars every year. They affect food, ornamental and industrial plants worldwide. Currently, there are 32 known species of these pathogens, all of which are composed of an unencapsidated, circular, single-stranded, non-coding RNA that is between 246-401 nucleotides (nt) long. These infectious RNA species replicate through an RNA-dependent rolling circle mechanism. Although they do not code for any known protein, viroids can obviate a plant's cellular defense mechanism and act as parasites, making them the smallest self-replicating genetic elements identified to date. ******RNA interference plays a central role in the pathogenesis of viroids so we propose to study the quasispecies nature of these pathogens. RNA interference elicits pathogenesis through base-pairing of vd-sRNA on host mRNAs. Consequently, it is clearly important to develop a method for following and understanding the evolution of the different haplotypes after infection, in addition to further strengthen our understanding of the related RNA silencing mechanism. Our long-term goal is to learn as much as possible on the biology of viroid species as a way of becoming a leader in the development of optimally resistant cultivars. In order to progress in this direction, our specific objectives are:******1. To study the behavior of the quasispecies under different growing conditions through time; and,***2. To identify the vd-sRNAs, and their respective host targets, as well as the plants' endogenous microRNAs that are affected during viroid infection.******All experiments will be performed with plant cultivars that are of importance for the Canadian agricultural sector. We expect to elucidate the definition of quasispecies under different growing conditions, and to highlight genes that play a key role in the pathogenesis of viroids in both tomato and grapevine. Our results should set the foundation for the elucidation of viroid pathogenesis, and should help finding a cure for these infections in addition to encouraging the use of viroids to advance the boundaries of life sciences.